Iron doesn't absorb well when you eat tablet form. Get liquid and have it with orange juice. Don't drink milk, don't have yoghurt or any calcium when you take it as it binds to calcium and you'll end up getting constipated and pooping it out!
Start salting your food if you don't already, I have low blood pressure too, drink lots of water and make sure you exercise a little everyday <--those are the very best things to quickly reverse low bp.
Iron binds oxygen to your blood. Low iron = low oxygen for baby and potential cognitive and developmental problems (ADHD & learning disabilities).
People too, often convulse if they are shallow breathing (think hot tubs, smoking etc). I used to be a life guard at the local pool - the boys would smoke grass and then jump into the hot tub. The heart rate goes up, they breath rapid & shallow and voila! fainting and convulsions (I know you aren't doing this lol you poor thing!! Bear with me here). Iron in liquid form and better circulation ie. walking, yoga, breathing deeply will help this condition. Salt your food and lots of water! Tea absorbs better than water and replaces electrolightic fluids. Just stick to mint, ginger, decaf roobios chai.
But iron pills?? Well if you're all bunged up over the toilet and still fainting, I feel for ya! Doctors are keen to hand out pills but did he tell you how hard it is to get iron to absorb?
I take mine in my morning shake: half a pack frozen spinach, 1 cup berries, 1 banana, 3vitamin c pills or a pack of 'EmergenC' powder, liquid iron, omega 3/6/9 oil, blend & drink. It's delicious and as long as you keep the yoghurt out, you won't get constipated either. $100 says you'll feel better in a week. But do get checked out, I hope everything is ok and it's not something more serious. Low bp combined with anemia is a terrible place to be when you're pregnant and you'll have to work at getting your health back if this is the cause of it all. Sending you